ANATOMY OF THE EAR 249 deficient above—the notch of Rivinus, The membrane is thin, and when examined with illumination has a pearly-grey colour with a triangular bright area, the cone of light, extending from the centre (the umbo) downwards and forwards. The membrane has an outer layer of squamous epithelium continuous with that of the meatus, a middle layer of fibrous, tissue which has radiating and circular fibres, and an inner layer of mucous membrane con- tinuous with the lining of the tympanic cavity. The fibrous tissue layer is deficient in the area of membrane bounded by the notch of Rivinus which, Fig. 127. Right tympanic membrane. Broken lines indicate medial relations, 1, Pars flaccida; 2, Pars tensa; 3, Cone of light; 4, Lateral process of malleus; 5, Handle of malleus; 6, Umbo; A, Head of malleus; B, Body of incus; C, Aditus; D, Long process of incus; E, Stapes; F, Stapedius tendon; G, Round window niche. being less tense, is known as the pars flaccida or ShrapnelPs membrane. The lower margins of this part are thickened and extend from the ends of the notch of Rivinus to the lateral process of the malleus forming the anterior and posterior folds of the membrane. The part of the drumhead containing fibrous tissue is known as the pars tensa. The outer surface of the tympanic membrane has a blood supply from the deep auricular branch of the maxillary artery. The inner surface receives branches from the posterior auricular _artery_ and. from the_maxiliary artery through its tympanic branch. .. . The nerve supply of the outer surface of the drumhead is similar to. that.. of the external meatus but the inner surface is supplied from the tympanic branch of the glossopharyngeal nerve. THE MIDDLE EAR The middle ear, a vertical cleft-like space in the temporal bone, includes the Eustachian tube, the middle ear or tympanic cavity and the aditus leading posteriorly to the mastoid antrum and air cells. Anteriorly the Eustachian tube opens into the nasopharynx from which the cleft develops in early fetal life.